Multiply, reduce to lowest terms, and write as a mixed number: $ 3\dfrac{1}{2} \times 5\dfrac{4}{5} $
$ = \dfrac{7}{2} \times \dfrac{29}{5}$ $ = \dfrac{7 \times 29}{2 \times 5}$ $ = \dfrac{203}{10}$ $ = 20 \dfrac{3}{10}$